Hi Gidd,
At the moment there is no way to link help functions to the Function keys, as these are mostly used by the browser you are using. You could try making a widget in JavaScript to catch these and link your own functions to it but I'm not sure how this will work out. You could always create a new incident in the Partner Portal for a feature request.
For a bubble with help text I suggest you use the new "Help Text Viewer" widget in the AppStore. I think it really matches what you are looking for, although it will give a mouseover (H) next to the field, instead of the mouseover being on the field itself.